1. Field of the Invention
The present invention relates generally to an optical storage device for reading or reading/writing information from and to an optical storage medium by use of an optical head and, more particularly, to an optical storage device for controlling a movement of a light beam.
2. Description of the Related Art
In an optical storage device such as an optical disk device etc, an optical head irradiates an optical storage medium with a light beam, thereby reading and writing information. In this optical storage device, a laser spot for scanning an information track on an optical disk is located on the information track. An objective lens of the optical head is therefore precisely moved in a track direction as well as in a focusing direction. A decrease in weight of the optical head is required of this optical storage device.
FIG. 16 is an explanatory diagram showing the prior art.
An optical disk 90 is formed with an information track in a spiral configuration or in a concentric configuration. An optical head 91 comprises a movable member 91-1 and a fixed member 91-2. The movable member 91-1 is provided with an objective lens 92, a focus actuator 93 for moving the objective lens 92 in the focusing direction, a track actuator 94 for moving the objective lens in the track direction, a lens position sensor 95, and a deflection mirror 96.
The fixed member 91-2 includes a light emitting diode and a divided-by-4 light receiving unit. A light beam emitted from the light emitting diode of the fixed member 91-2 is incident upon the objective lens 92 via the deflection mirror 96, and falls upon the optical disk 90. The light beam reflected from the optical disk 90 is incident upon the fixed member 91-2 via the objective lens 92 and the deflection mirror 96.
In the fixed member 91-2, the reflected light beam is received by the divided-by-4 light receiving unit in which a light receiving element is divided by 4. A signal generating circuit 98 calculates an output of the divided-by-4 light receiving unit, and generates a focus error signal FES, a track error signal TES and an ID signal etc. The focus error signal FES indicates a focusing-directional deviation of the light beam from the track.
A DSP-based control circuit 99 focus-servo-controls the focus actuator 93 on the basis of the focus error signal FES, and thus adjusts a focusing position of the light beam. The track error signal TES indicates a track-directional deviation of the light beam. A control circuit 99 track-servo-controls the track actuator 94 on the basis of the track error signal TES, and thus locates the light beam on the track.
A motor 97 constructed of a linear motor etc moves the movable member 91-1 of the optical head 91 in a track traversing direction of the optical disk 90. The optical head 91 is thereby subjected to a coarse seek process.
In this construction, the lens position sensor 95 generates a lens position signal LPOS indicating a position of the objective lens 92. This lens position signal LPOS is, when the optical head 91 is moved by the motor 97 (when in the coarse seek process), used for locking the objective lens 92. More specifically, when in the coarse seek process, a present position is detected based on the track error signal TES, thereby executing the seek control. Therefore, if the objective lens 92 is not fixed, the present position is unable to be accurately detected. Hence, the control circuit 99 controls the track actuator 94 on the basis of the lens position signal LPOS. The objective lens 92 is thereby locked.
Further, the lens position signal LPOS is used for, with the movement of the objective lens 92, when implementing a track access process (a track jump process), detecting the position of the objective lens. Moreover, the lens position signal LPOS is used for, when performing eccentricity compensation control of the optical disk, detecting the position of the objective lens 92.
Thus, the seek control is carried out so that the light beam is disposed in a central position of the objective lens 92 by use of the lens position signal LPOS. The generation of the thus-used lens position signal LPOS involves providing the movable member 91-1 of the optical head 91 with the lens position sensor 95.
There arise, however, the following problems inherent in the prior art.
First, the optical head 91 is light in weight, which is better for the optical head effecting a high-speed seek to a target track. Therefore, the movable member 91-1 of the optical head 91 is mounted with only parts needed for making the movable member 91-1 movable. The movable member 91-1 is, however, required to be mounted with the lens position sensor 95, and hence the weight of the movable member 91-1 can not be reduced. It is therefore difficult to speed up the seeking process.
Second, since the lens position sensor 95 consists essentially of the light emitting unit and the light receiving unit, the costs thereof are high. Consequently, the optical storage device has a difficulty to be constructed at low costs.